Segmented core for an inductive proximity sensor

ABSTRACT

An inductive proximity sensor for sensing the presence of target based on a change of inductance in the sensor. The sensor includes a coil and a core formed of a permeable material so as to form an electromagnetic field when the coil is electrically driven. The core has a base, a central post, an outer wall, and at least one slot. The central post extends distally from the base and through the coil and defines a distal end. The outer wall extends distally from the base and around the coil and also defines a distal end. The slot or slots are for enhancing the performance of the sensor by reducing eddy current losses in the core. Each slot extends at least partially along a path defined from the distal end of the outer wall to the base and from the base to the distal end of the central post.

FIELD OF THE INVENTION

The present invention generally relates to inductive proximity sensorsand, more particularly, to variable reluctance-type inductive proximitysensors and methods of detecting the proximity of an object.

BACKGROUND OF THE INVENTION

Proximity sensors have many different applications in many differentindustries. In the aerospace industry, for example, proximity sensorscan be used within an aircraft to detect the position of various movablecomponents. More specifically, proximity sensors can be used to detectthe position of aircraft landing gear, landing gear doors, spoilers,passenger doors, and/or cargo doors. In this regard, such proximitysensors can be used to indicate aircraft conditions such asweight-on-wheels, landing gear up/down, doors open/closed, and/orspoilers stowed/not stowed.

As will be appreciated, proximity sensors can be configured to detectthe presence of an object in accordance with a number of differenttechniques including, for example, variable reluctance, eddy currentloss, saturated core, and the Hall effect. In general, a sensor includesa core of a highly-permeable metal and an inductive coil. While theshape of the core can vary, in one typical configuration, the core cancomprise a central post and an outer cylindrical wall. The coil iswrapped around the central post and is contained within the outercylindrical wall.

In accordance with a variable-reluctance proximity detection technique,an external AC current source drives the coil of the proximity sensor toform an electromagnetic circuit with the core. When a permeable and/orconductive object is brought or otherwise moved into the alternatingmagnetic field caused by the electromagnetic circuit, the reluctance(i.e., air gap resistance) between the object and the proximity sensorchanges, or more particularly, decreases. As the reluctance decreases,the inductance of the coils increases. This increase can then bemeasured to thereby detect the proximity of the object.

The effective range of the sensor is dependent on the amount of changein inductance created by the object as it approaches. The greater thechange the faster the sensor can detect the object both in sense ofdistance between the object and sensor and the time required to measurethe inductance difference.

However, eddy currents are created in the core by the electromagneticcircuit. The eddy currents resist change in the magnetic field. Thisresistance to change reduces the inductance, and thus the signal, causedby the object entering the magnetic field. Furthermore, the eddycurrents also provide a resistive loss to the AC circuit. Both thedecrease in inductance and increase in resistance contribute to reducebandwidth of the circuit and increase the time required to make ameasurement. Conversely, the lost signal could be used to sense theobject at a greater distance.

BRIEF SUMMARY OF THE INVENTION

The present invention addresses the above needs and achieves otheradvantages by providing an improved proximity sensor having a segmentedmagnetic core to enhance the range and measurement cycle of the sensor.Generally, the proximity sensor includes at least one coil and a core.The core defines at least one slot. Advantageously, the slot or slotsreduce eddy current losses by disrupting the flow of eddy currentswithin the core. Segmenting the core can be accomplished in several waysand therefore the invention has numerous embodiments.

For example in one embodiment, the present invention includes aninductive proximity sensor for sensing at least the presence of a targetadjacent to the sensor based on a change of inductance in the sensorrelative to the absence of the target adjacent the sensor. The coil iscapable of being electrically driven to generate a magnetic field. Thecore is formed of a permeable material so as to form an electromagneticfield when the coil is electrically driven. The core defines a base, acentral post, an outer wall, and at least one slot. The central postextends distally from the base and through the coil and defines a distalend. The outer wall extends distally from the base and around the coiland also defines a distal end. Each slot extends at least partiallyalong a path defined from the distal end of the outer wall to the baseand from the base to the distal end of the central post. The slot orslots enhance the performance of the sensor by reducing eddy currentlosses in the core.

The number of slots may vary depending on the embodiment. For examplepurposes and not as a limitation, the core may define four or eightslots. Also, depending on the embodiment, the degree to which each slotextends along the path defined from the distal end of the outer wall tothe base and from the base to the distal end of the central post mayvary. Again for example purposes and not as a limitation, at least oneslot may fully extend along the path. The depth of which each slotextends into the permeable material of the core may vary according tothe embodiment. For example, in one embodiment each slot may extendthrough the outer wall. In another embodiment, each slot may extendthrough the base. Conversely, in another embodiment each slot may extendonly partially into the central post.

In another aspect, the central post may also include a solid distalarea. The solid distal area advantageously maintains some of thecross-sectional area, and thus the magnetic path area, reduced by theslot or slots in the central post.

In yet another embodiment of the present invention, the sensor includesat least one coil and a laminated core. In general, the core is roundand includes two or more pie-shaped sections and one or more insulatinglayers. Each section has a base, a central post, and an outer wall. Thecentral post extends distally from the base and through the coil anddefines a distal end. Similarly, the outer wall extends distally fromthe base and around the coil and defines a distal end. The one or moreinsulating layers separate the adjacent pie-shaped sections from eachother. The pie-shaped sections and insulating layers together form anintegrated laminated core. The insulating layers enhance the performanceof the sensor by disrupting the flow of eddy current within the core.

The number of pie-shaped sections may vary depending on the embodiment.For example purposes and not as a limitation, the core may define fouror eight pie shaped sections.

In another aspect of the present invention, the sensor may furtherinclude a housing and an end plate. The housing and end plate, together,enclose the core and coil.

The present invention has several advantages. The slots in the corereduce eddy current losses and thus enhance the cycle time and range ofthe sensor. The solid distal area on the central post limits the lostcross-section area caused by the slots. Similarly, the insulating layersin the laminated core reduce eddy currents losses and thus enhance thecycle time and range of the sensor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a quadrant perspective view of the sensor according to oneembodiment of the present invention;

FIG. 2 is a perspective view of one embodiment of the present invention,wherein the core defines 8 slots;

FIG. 3 is a top view of the core illustrated in FIG. 2;

FIG. 4 is a bottom view of the core illustrated in FIG. 2;

FIG. 5 is a perspective view of another embodiment of the presentinvention, wherein the core defines 4 slots;

FIG. 6 a is a perspective view of yet another embodiment of the presentinvention having a core defining 4 pie-shaped sections, wherein onepie-shaped section is removed; and

FIG. 6 b is a perspective view of the pie-shaped section removed fromthe core in FIG. 6 a.

DETAILED DESCRIPTION OF THE INVENTION

The present inventions now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the inventions are shown. Indeed, these inventions may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

In general, as shown in the figures, the present invention includes aninductive proximity sensor 10 for sensing at least the presence of atarget 11 adjacent to the sensor 10 based on a change of inductance inthe sensor 10 relative to the absence of the target 11 adjacent to thesensor 10. According to one embodiment as shown in FIG. 1, the sensor 10includes a coil 14, and a core 15. The coil 14 is wrapped around acentral post 17 of the core 15 and within an outer wall 18 of the core15. The core 15 is made of a permeable material and, as best seen inFIGS. 2 through 4, defines a base 16, the central post 17, the outerwall 18, and at least one slot 19 in the permeable material. The centralpost 17 extends distally from the base 16 and through the coil 14 anddefines a distal end 20. The outer wall 18 extends distally from thebase 16 and around the coil 14 and defines a distal end 21. Inoperation, the coil 14 is capable of being electrically driven by anexternal AC current source in order to create an alternating magneticfield through and around the core 15. As illustrated, the base 16 maydefine a number of openings to provide a path for an electricalconnection between the coil 14 and the current source.

The slot or slots 19 in the permeable material extend at least partiallyalong a path defined from the distal end 21 of the outer wall 18 to thebase 16 and from the base 16 to the distal end 20 of the central post17. The slot or slots 19 are for enhancing the performance of the sensor10 by reducing eddy current losses in the core 15. While not intendingto be bound by any particular theory, it is believed that the slots 19disrupt the eddy currents that would be induced in the core 15, by themagnetic field through and around the core 15, and would oppose themagnetic field. In particular, without the slots 19, the eddy currentswould circulate around the longitudinal axis of the core 15, risingapproximately linearly from zero at the axis. The slots 19 are generallyperpendicular to the eddy current paths in conventional proximitysensors and thus prevent or at least disrupt the eddy currents andincrease the inductance in the sensor 10.

The number of slots 19 defined in the core 15 may vary. For examplepurposes only and not as a limitation, the core 15 may define four, asshown in FIG. 5, or eight slots 19, as shown in FIGS. 2 through 4. Alsothe degree in which each slot 19 extends along the path defined betweenthe two distal ends 20, 21 may vary. For example, a slot 19 may fullyextend along the entire path, as in FIG. 5. Alternatively the slots 19may extend entirely along the outer wall 18 and base 16 portions of thepath but extend short of the distal end 20 of the central post 17 alongthat portion of the path, as best seen in FIG. 3 and 4 and for reasonsexplained further below. As illustrated, the portion of the slots 19along the outer wall 18 and base 16 may be through-slot portions, i.e.that portion of the slot 19 exists through the entire depth of thematerial in those areas. However the slot 19 does not need to extendentirely through the thickness of the outer wall 18 or the base 16. Itis preferred that the portion of the slot 19 along the central post 17only partially extend into the material of the central post 17. Thisallows for the core 15 to remain integrated. Moreover, leaving thecenter of the post 17 solid has a minimal effect on eddy currents whenthe slots 19 are disrupting the eddy currents away from the center. Thecenter of the central post 17 is also the longitudinal axis of the core15. As stated above, the eddy currents are weakest and approaching zeronear and at the longitudinal axis.

The width of each slot 19 is relatively thin. Limiting the width of eachslot 19 is advantageous for mechanical considerations such asmaintaining the stiffness and strength of the core 15. Furthermore,limiting the width of each slot 19 is also advantageous forelectromagnetic considerations. It is preferable to limit the amount ofpermeable material that is displaced by the slots 19 because the amountof material is directly proportional to the reluctance in the sensor 10.Moreover, the widths of the slots 19 are not significant to the slots'19 capability to disrupt the eddy currents. In theory, any break in thepermeable material is significant enough to alter or disrupt the flow ofan eddy current. One practical consideration for the width of each slot19 is the capability of the machining or manufacturing process forforming the slot or slots 19 in the core 15. For example purposes only,the slot or slots 19 may be formed by a milling tool. According to oneembodiment, the width of each slot 19 is approximately 0.020 inches.

Even by limiting the width of each slot 19, the portions of the slots 19in the central post 17 do have a compromising effect on the inductancein the sensor 10. Although the slots 19 reduce the eddy current losses,they also reduce the cross-sectional area of the central post 17, andthus the magnetic path area. As such, the post 17 may be formed withoutany slots. The central post 17 of the core 15 with the surrounding coil14 is similar to a solenoid. For a solenoid, inductance is directlyproportional to the permeability of the core material andcross-sectional area of the post 17.

In some embodiments and as shown in FIG. 2 as compared to FIG. 5, thecore 15 may also have a solid foot or distal area 23. According to theseembodiments, the slots 19 do not extend to the distal end 20 of thecentral post 17. The solid distal area 23 extends and defines athickness from the end of the slots 19 to the distal end 20 of thecentral post 17. In theory, the thickness of the solid distal area 23 isa compromise of increasing the magnetic path area versus increasing theeddy current losses. As shown, the solid distal area 23 may have abeveled edge 24. The beveled edge 24 reduces the thickness of the soliddistal area 23 as it extends away from the longitudinal axis of the core15, where eddy currents would be the greatest. For example purposes onlyand not as limitation, the solid distal area 23 may have a thicknessbetween approximately 0.01 inches and 0.02 inches. The beveled edge 24may be a 45 degree bevel. The distance from the distal end 20 to thebase 16 may be between approximately 0.330 inches to 0.340 inches.

In another embodiment of the present invention, the sensor 10 has alaminated core 30 and a coil 14. As illustrated in FIG. 6, the core 30is generally round and defines two or more pie-shaped sections 31 andone or more insulating layers 32. Each pie-shaped section 31 includes abase 34, a central post 35, and an outer wall 36. The central post 35extends distally from the base 34 and through the coil 14 and defines adistal end 38. Similarly, the outer wall 36 extends distally from thebase 34 and around the coil 14 and defines a distal end 39. The one ormore insulating layers 32 separate the adjacent pie-shaped sections 31from each other. The pie-shaped sections 31 and insulating layers 32together form an integrated laminated core 30 for enhancing theperformance of the sensor 10 by reducing eddy current losses in the core30.

The number of pie-shaped sections 31 may vary depending on theembodiment. For example purposes and not as a limitation, the core 30may define four, as illustrated, or eight pie shaped sections 31.

As stated above, the adjacent pie-shaped sections 31 are separated by atleast one insulating layer 32. Preferably the insulating layer or layers32 is an adhesive that can bind the pie-shaped sections 31 together.

Again, while not intending to be bound by any particular theory, it isbelieved that the insulating layers 32 disrupt the eddy currents thatwould be induced in the core 30 and oppose the magnetic field. Similarto the slots 19 discussed above, without the insulating layers 32, theeddy currents would circulate around the longitudinal axis of the core30, generally rising from zero at the axis. The insulating layers 32 aregenerally perpendicular to the anticipated eddy current paths and thusprevent or at least disrupt the eddy currents and increase theinductance in the sensor 10.

In another aspect of the present invention, the sensor 10 may also havea housing 12 and end plate 13. Together the housing 12 and end plate 13provide an overall enclosure for the sensor 10, as best shown in FIG. 1.

The present invention has several advantages. The slots 19 in the core15 reduce eddy current losses and thus enhance the cycle time and rangeof the sensor 10. The solid distal area 23 of the central post 17compensates for some of the lost cross-section area caused by the slotor slots 19. Similarly, the insulating layers 32 in the laminated core30 reduce eddy currents losses and thus enhance the cycle time and rangeof the sensor 10.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1. An inductive proximity sensor for sensing at least the presence of atarget adjacent to the sensor based on a change of inductance in thesensor relative to the absence of a target adjacent the sensor, saidsensor comprising: at least one coil capable of being electricallydriven to generate a magnetic field and; a core formed of a permeablematerial so as to form an electromagnetic field when the coil iselectrically driven, the core defining, a base, a central post extendingdistally from the base and through the coil and defining a distal end,an outer wall extending distally from the base and around the coil anddefining a distal end, and at least one slot in the permeable materialfor enhancing the performance of the sensor by reducing eddy currentlosses in the core, wherein each slot extends at least partially along apath defined from the distal end of the outer wall to the base andpartially from the base to the distal end of the central post.
 2. Thesensor of claim 1, wherein the core further defines four slots.
 3. Thesensor of claim 1, wherein the core further defines eight slots.
 4. Thesensor of claim 1, wherein a portion of each slot along the outer wallextends completely through the outer wall.
 5. The sensor of claim 1,wherein a portion of each slot along the base extends completely throughthe base.
 6. The sensor of claim 1, wherein the central post has a soliddistal area.
 7. The sensor of claim 1, further comprising a housing andan end plate that together enclose the coil and the core.
 8. Aninductive proximity sensor for sensing at least the presence of a targetadjacent to the sensor based on a change of inductance in the sensorrelative to the absence of a target adjacent the sensor, said sensorcomprising: at least one coil capable of being electrically driven togenerate a magnetic field and; a core formed of a permeable material soas to form an electromagnetic field when the coil is electricallydriven, the core defining, a base, a central post extending distallyfrom the base and through the coil and defining a distal end, an outerwall extending distally from the base and around the coil and defining adistal end, and at least one slot in the permeable material forenhancing the performance of the sensor by reducing eddy current lossesin the core, wherein each slot extends at least partially along a pathdefined from the distal end of the outer wall to the base and from thebase to the distal end of the central post, and wherein at least oneslot fully extends along the path defined from the distal end of theouter wall to the base and from the base to the distal end of thecentral post.
 9. An inductive proximity sensor for sensing at least thepresence of a target adjacent to the sensor based on a change ofinductance in the sensor relative to the absence of a target adjacentthe sensor, said sensor comprising: at least one coil capable of beingelectrically driven to generate a magnetic field and; a core formed of apermeable material so as to form an electromagnetic field when the coilis electrically driven, the core defining, a base, a central postextending distally from the base and through the coil and defining adistal end, an outer wall extending distally from the base and aroundthe coil and defining a distal end, and at least one slot in thepermeable material for enhancing the performance of the sensor byreducing eddy current losses in the core, wherein each slot extends atleast partially along a path defined from the distal end of the outerwall to the base and from the base to the distal end of the centralpost, and wherein at least a portion of each slot extends partiallythrough the central post.
 10. A core formed of a permeable material soas to form an electromagnetic field when a coil wrapped around the coreis electrically driven as part of an inductive proximity sensor, saidcore comprising: a base, a central post extending distally from the baseand through the coil and defining a distal end, an outer wall extendingdistally from the base and around the coil and defining a distal end,and at least one slot defined in the permeable material for enhancingthe performance of the sensor by reducing eddy current losses in thecore, wherein each slot extends at least partially along a path definedfrom the distal end of the outer wall to the base and partially from thebase to the distal end of the central post.
 11. The core of claim 10,further comprising four slots.
 12. The core of claim 10, furthercomprising eight slots.
 13. The core of claim 10, wherein a portion ofeach slot along the outer wall extends completely through the outerwall.
 14. The core of claim 10, wherein a portion of each slot along thebase extends completely through the base.
 15. The core of claim 10,wherein the central post has a solid distal area.
 16. A core formed of apermeable material so as to form an electromagnetic field when a coilwrapped around the core is electrically driven as part of an inductiveproximity sensor, said core comprising: a base, a central post extendingdistally from the base and through the coil and defining a distal end,an outer wall extending distally from the base and around the coil anddefining a distal end, and at least one slot defined in the permeablematerial for enhancing the performance of the sensor by reducing eddycurrent losses in the core, wherein each slot extends at least partiallyalong a path defined from the distal end of the outer wall to the baseand from the base to the distal end of the central post and wherein atleast one slot fully extends along the path defined from the distal endof the outer wall to the base and from the base to the distal end of thecentral post.
 17. A core formed of a permeable material so as to form anelectromagnetic field when a coil wrapped around the core iselectrically driven as part of an inductive proximity sensor, said corecomprising: a base, a central post extending distally from the base andthrough the coil and defining a distal end, an outer wall extendingdistally from the base and around the coil and defining a distal end,and at least one slot defined in the permeable material for enhancingthe performance of the sensor by reducing eddy current losses in thecore, wherein each slot extends at least partially along a path definedfrom the distal end of the outer wall to the base and from the base tothe distal end of the central post and wherein a portion of each slotalong the central post extends partially through the central post.